The present invention relates to an image forming apparatus, such as a copying apparatus or a printer, having a charger using an electrophotographic process.
A conventional image forming apparatus using an electrophotographic process, such as a copying apparatus or a printer, includes an image forming section for forming an image based on image data and outputting the image onto a recording medium such as a paper sheet.
The image forming section has a photosensitive body which retains an electrostatic latent image corresponding to image data. In the image forming apparatus, the following elements are disposed around the photosensitive body in order in its rotational direction: a charger for charging a surface of the photosensitive body at a uniform potential; an optical scanning device, such as a laser exposure device, for exposing the charged photosensitive body to form an electrostatic latent image; a developing device for applying a developer, or a toner, to the electrostatic latent image to form a toner image; a transfer charger for transferring the toner image on the photosensitive body onto a recording medium such as a paper sheet; a separating charger; a cleaning device for removing toner remaining on the photosensitive body after the transfer of the toner image; and a charger erase device for eliminating charge remaining on the photosensitive body.
The charger included in the image forming section is disposed with a predetermined distance from the surface of the photosensitive body. The charger electrifies the surface of the photosensitive body by means of a corona charger.
In the image forming apparatus having the charger, a total current of a predetermined level or more, which matches with the performance of the charger, is necessary for obtaining good electrification properties of the photosensitive member. In particular, in a life-time period of a charging wire, dispersed toner or an ozone product adheres to the charging wire and non-uniform electrification may occur. To prevent this, a set value of total current is increased.
However, since the amount of produced ozone is proportional to the total current, the amount of produced ozone increases if the set value of total current is raised in order to prevent non-uniform electrification. As a result, the concentration of ozone remaining in the charger increases accordingly. Thus, non-uniformity due to ozone increases.
Besides, during a copying operation or in a standby state, outside air is taken in for the purpose of cooling the electric components. This produces a wind within the apparatus and disperses ozone. If the power to the image forming apparatus is stopped, high-concentration ozone remains in the charger. Thereby, non-uniform electrification due to ozone occurs partly on the photosensitive body facing the charger. Consequently, when an image is formed the next time, a defective image with stripes may be formed.
The object of the present invention is to provide an image forming apparatus and an image forming method, wherein non-uniform electrification is prevented and a defective image is prevented from being formed as a result of non-uniform electrification due to ozone.
In order to achieve the object, the present invention may provide an image forming apparatus for forming an image, the image forming apparatus including a photosensitive body which forms an electrostatic latent image, the apparatus comprising: charging means for charging the photosensitive body at a predetermined potential; first control means for setting a total current flowing in the charging means at a first set value during an image forming operation; and second control means for setting, when turn-off of power to the image forming apparatus has been instructed, the total current flowing in the charging means at a second set value different from the first set value, and controlling a finishing operation which leads to the turn-off of power.
The invention may provide an image forming method for an image forming apparatus for forming an image, the image forming apparatus having a charger which charges a photosensitive body for formation of an electrostatic latent image at a predetermined potential, the method comprising: setting a total current flowing in the charger at a first set value during an image forming operation in the image forming apparatus; setting, when turn-off of power to the image forming apparatus has been instructed, the total current flowing in the charger at a second set value lower than first set value; and executing a control to turn off the power to the image forming apparatus, including a control to turn off the total current flowing in the charger, after a predetermined time period has passed since the turn-off of power to the image forming apparatus was instructed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.